: 10w40 in N*

12-22-07, 08:32 PM
Is it OK to use 10w40 in a northstar engine? The manual calls for 5w30 and 10w30, but doesn't say anything about 10w40.

My car has 70k miles and is a 2000 deville. Will be doing some hard driving the next few days for a road trip. By hard driving, I'm talking WOT driving to pass cars and trucks in two lane highways. Along with a 22hr drive.

12-22-07, 08:50 PM
Is it OK to use 10w40 in a northstar engine?
No. Use 5W30 or 10W30.

12-22-07, 09:45 PM
10w30 and 10w40 is the viscosity range. It doesn't benefit you to put 10w40 in. 10w40 also tends to sludge easier than 10w30.

12-22-07, 10:24 PM
If I can go to Florida and back twice a year, run the snot out of the car otherwise, do WOT's, and get 3,500 miles to the quart of 5W-30 synthetic in temperate climates, so can you. Your manual recommends 5W-30 in all temperatures and allows 10W-30 above ?? 20 degrees or so. Whatever floats your boat.

Higher viscosity ratings than recommended have absolutely NOTHING to do with wear considerations in an engine that is not originally spec'd for them. Using them may well be detrimental to engine life.

It generally costs $$$ to try and outguess the design engineers.

12-23-07, 10:54 AM
If you already have it then it won't hurt anything to use it.

Otherwise I would use 5/30, or 10/30 in warm climate like Florida.

12-26-07, 12:27 PM
I've used 15W-50 Mobile One in both my Seville and Deville during the summer months if I know I will be doing a large amount of high speed driving, i.e. to and from northern Michigan and Texas. I've found that at highway speeds the engine seems to run smoother. Possibly placebo effect but it has never hurt anything.

12-27-07, 02:44 AM
You will do no damage to your engine by using a heavier grade oil, as long as it's not extremely heavy. 15w50, as in the above example, is still thinner warm than 5w30 is when cold, so it will present no problem at all.